forming head for dry forming a fibrous web

ABSTRACT

The invention relates to a forming head for dry forming a fibrous web, which forming head is positioned above a forming wire opposite a suction unit. The forming head is divided into at least two independent interconnected distribution units, each of which comprises at least one revolving roller provided with protruding spikes. By dividing the forming head into a plurality of interconnected distribution units, a more efficient disintegration of agglomerates, shadows and/or lumps in the fibre material is achieved compared to the known forming heads, thereby ensuring a more homogenous final product.

The present invention relates to a forming head for dry forming a fibrous web, the forming head being positioned above a forming wire opposite a suction unit. The present invention also relates to a method of using said forming head.

Various forming head of this type are known, for instance from European Patent Application 0159618. This application describes a forming head provided with a bottom net or sieve having a plurality of openings. In order to ensure the passage of the fibres through the bottom of the forming box it is suggested to use wings, rollers or other scraping or brushing devices, which in an active manner removes fibres from the sieve at the bottom of the forming head. A suction unit is provided underneath the forming wire for drawing the fibres through the bottom and onto the forming wire. Although such mechanical devices do give an increase in the capacity, the obtained increases are not satisfactory and attempts have been made through many years to increase the capacity further.

The size of the openings in the mesh or sieve in the bottom of the forming box is decided by the fibres, which are to be distributed on the forming wire. This is particularly relevant in relation to the use of cellulose fibres in the manufacture of paper products including absorbing products, such as napkins. Thus, there has been a limitation in the length of the fibres used.

In an attempt to overcome the problem with fibre length WO 99/36623 describes a forming head with an open bottom, i.e. without a bottom mesh or sieve. The distribution of fibres is carried out by a plurality of revolving spike rollers. Said spikes are arranged to partly hold the fibres back against the effect from the suction of the underlying suction unit. The cloud of fibres which is formed inside the forming head of single fibres, which are slit up and mixed in the air stream, are transferred down onto the underlying wire by the application of the revolving spike rollers. This increases the capacity of the forming apparatus significantly. However, the inventor has discovered that agglomerates of fibres may pass the spike rollers without being torn sufficiently apart by the spikes, resulting in an uneven distribution of fibres on the forming wire and therefore in an inhomogeneous final product.

Another problem with the known forming heads is that they are extremely expensive. Therefore, the manufactures prefer to use one or more forming heads which can be used for the production of many different webs, instead of using a forming head having a design which is optimal for the production of a specific web. Thus the forming head conventionally used is not specifically designed for a given product, resulting in a web having a lower quality than desired.

Thus there is a need for a forming head, which is capable of meeting the desired optimal production requirements without impairing the quality of any of the resultant webs.

It is therefore a first aspect of the present invention to provide a modular forming head, which is strong and which comprises a number of distribution units which can be readily assembled into a complete forming head and allow greater control and adjustment between adjacent distribution units.

It is a second aspect according to the present invention to provide a forming head which ensures that agglomerates, shadows and/or lumps of fibres are torn apart to a higher degree than hitherto known.

It is a third aspect according to the present invention to provide a forming head according to the present invention, which ensures an even distribution of fibres on the forming wire in a dry-forming apparatus without compromising the capacity of the fibre distributor.

It is a fourth aspect according to the present invention to provide a forming head which is reliable in operation and which allows for longer time between overhauls or maintenance.

It is a fifth aspect according to the present invention to provide a forming head having spikes which are more resistant to breakings than hitherto known.

It is a sixth aspect according to the present invention to provide a forming head capable of easily being adapted to different fibre types and fibre length.

It is a seventh aspect according the preset invention to provide a forming head capable of forming different webs and/or mats without compromising the capacity of the fibre distributor.

This is achieved according to the present invention in that the forming head is divided into a plurality of independent and interconnected distribution units each of which comprises at least one revolving roller, which are provided with protruding spikes.

As the interconnected distribution units are detachable mounted in the forming head, it is ensured that the forming head is a modular forming head capable of being adapted and modified in order to meet the production requirements of many different webs and at the same time obtain a high quality of manufacture as each distribution unit can be individually and optimally designed to the material used and the desired final product.

The modular forming head according to the present invention results in a system having a number of different individual distribution units, which readily and arbitrarily can be assembled into a complete forming head which allow greater control and adjustment between adjacent distribution units than known until now.

Thus, the present invention provides a forming head that simplify installation and assembly of said forming head, and enable users to arbitrarily add and/or adjust internal components. The different distribution units of the forming head according to the invention may furthermore be designed at the customer's demands.

The different components, distribution units and revolving rollers may be delivered to and assembled at the production site, for stand alone use or may be attached to structural frame elements to provide a forming head that is integrated with other relevant elements of the production plant.

Installers and/or end users may also modify the configuration and/or location of the different distribution units and its components as desired.

The forming head according to the invention is formed from a plurality of distribution units assembled by way of connector elements. Preferably connector elements comprise a bolt-type member inserted into holes in the walls and are fixed with nuts however other connector elements known to the person skilled in the art is also contemplated in the present invention.

A forming head according to the invention can therefore be constructed to be able to arbitrarily handle long fibres and/or particles and/or short fibres.

Conventional forming heads for manufacturing an air laid web are always designed specifically to meet the requirements of the resulting web using the desired fibers, and if e.g. the a different fiber length is requested said forming head is not capable of meeting the requirements of said fibres. Thus, the use of conventional forming heads is limited to a specific application. Using the forming head according to the present invention solves this problem as each distribution unit is designed to be detachably secured and replaceable. When a user wishes to manufacture a different product using different fibers or simply different conditions are needed in the forming head in order to ensure that the web has the desired properties, the user simply replaces, removes or adds one or more of the distribution units with one or more different distribution units depending on the conditions and requirements.

By providing a forming head according to the present invention which comprises a number of distribution units it is ensured that the distribution units readily can be assembled into a complete forming head meeting the optimal production conditions needed for the resultant web. Thus, each distribution unit is a “plug and go” unit, which can be removed and exchanged, swiftly by hand, replaced by another unit or simply removed or added from the forming head.

The distribution unit(s) can also be constructed to meet specific and unique production requirements. Such requirements could e.g. be related to the final product, the fibre material used or the airflow supplied in the forming head. In this respect each distribution unit can be designed optimally, ensuring that the specific unit is best suited for distributing and mixing the fibres.

As an example can be mentioned that one of the distribution units can be designed to give a very high impact force to the fibre material supplied to the unit, whereas another distribution unit can be designed to ensure a high degree of mixing of the fibre material supplied to the forming head.

Thus, the forming head allows greater control and adjustment between adjacent distribution units than known until now.

Furthermore, by having a forming head that comprises at least two independent distribution units, the inventor has surprisingly found that a more efficient disintegration of fibres is achieved compared to the known forming heads.

This is due to the fact that the disintegration of agglomerates, shadows and/or lumps of fibrous material are influenced by strokes from spikes on the revolving rollers. When the spikes on the revolving roller impact with e.g. the agglomerates the impact force will ensure that said agglomerates are disintegrated. By having more than one distribution step it has surprisingly been found that agglomerates, shadows and/or lumps that are not disintegrated in the first distribution step will be disintegrated in the underlying unit.

Using the forming head according to the present invention will thereby not only ensure, that all agglomerates, shadows and/or lumps in the fibrous material will be removed but also that the fibres will completely opened and separated.

The present invention therefore provides the possibility of producing uniform webs at higher speeds than heretofore possible and/or to improve the uniformity of webs made at existing speeds. This is assumed that the very high degree of separation caused by the different distribution steps improves the mixing of fibres in the forming head to give these improved results.

When a forming head according to the present invention is applied in a dry-forming apparatus, it has furthermore been possible to form a fibrous product, where problems are avoided with the variation of the thickness over the width of the product.

As used herein, the term “distribution unit” refers to a distribution unit, which is capable of standing alone i.e. function as a forming head without the control or influence of another distribution unit.

Thus, the forming head according to the invention does not only provide a more efficient opening and disintegration of fibres than hitherto known, but will also ensure that that fibre lumps or oversized fibres are prevented from being laid down on the forming wire and that the fibres are mixed homogenously before they are placed on the forming wire. The forming head according to the invention thereby achieves an even distribution of fibres on the forming wire without reducing the capacity of the fibre distributor.

In order to achieve further disintegration of the fibres and thereby promote a more even distribution, the at least one revolving roller with belong spikes in at least one of the distribution units can advantageously cover the entire sectional area of the distribution unit when seen in a mainly horizontal plane. Thereby it is ensured that the fibres are partly retained in the distribution unit whereby the remaining agglomerates, shadows and/or lumps will be returned to the distribution unit in question, providing that e.g. the agglomerates is comminuted and disintegrated rather than being sucked down to the forming wire by the suction unit.

This is preferably the distribution unit placed just above the forming wire, but could in an alternative embodiment be any of the distribution unit or several of the distribution units.

However, in a preferred embodiment the sectional area of at least one of the distribution units is only covered partly by the at least one revolving roller with belonging spikes. The inventors of the present invention have surprisingly discovered that this ensures that the air circulation and air direction is reverse providing a more even and homogenous distribution of fibres compared to a forming head where the sectional area of the distribution units are completely covered by the revolving rollers. It is especially preferred if the percentage of the sectional area covered by revolving rollers in said distribution unit is between about 30% to about 80%, preferably about 65%.

In order to obtain that only a part of the sectional area of the distribution unit(s) is covered by the at least one revolving rollers it is possible simply to place fewer revolving rollers in the distribution unit and/or by regulating the dimension of the spikes on the revolving rollers. However, it is also possible either alone or in combination to regulate the dimension and/or length of the revolving rollers.

The person skilled in the art will based on the material used and the final product in combination with the information provided in the present application be able to find the optimal requirements for the different distribution units and thereby the forming head according to the invention.

In a preferred embodiment according to the present invention the at least one distribution unit comprises a plurality of revolving roller arranged in a substantially horizontal plane. As the fibrous material in this respect will be forced to pass the revolving rollers, it is ensured that the fibres are symmetrically laid down on the forming wire, forming a final product with a homogeneous thickness over the width of the forming wire.

All revolving rollers in a distribution unit are preferably driven by a single engine and a synchronous transmission belt.

Thereby is obtained the beneficial effect that the revolving rollers can be placed so that the outer ends of the spikes describe circles that overlap each other e.g. meshes like toothed gear. Such an embodiment has the advantage that the revolving rollers can be placed closer to each other, whereby the fibres can be influenced by more than one spike at a time. This will provide a higher impact force on the agglomerates, lumps and/or shadows, enabling a better disintegration of the fibrous material. Furthermore, when the outer ends of the spikes are transferred in-between each other, it becomes possible to manufacture a fibrous tissue using very short fibres, for instance with lengths down to 3 mm. Hereby it becomes possible to achieve a product with a very homogeneous profile in the sectional direction as well as in the longitudinal direction.

The closer the spikes are placed to each other on the revolving rollers, the more efficient will the spikes return agglomerates, lumps and/or shadows to the distribution unit. In this manner the fibre clumps or clusters of fibres are retained by the spike rollers and separated or disintegrated in a graduated fashion as these retained fibres are returned by the spikes to the distribution unit rather than being sucked down to the forming wire by the suction unit.

Alternatively the revolving rollers can be placed so that the outer ends of the spikes describe circles that do not overlap each other. This is especially advantageously when the forming head according to the present invention handles long fibres, for instance with a length of 60 mm or more as the circles which define the outer ends of the spikes substantially just touch each other or are a little shifted from each other. In this respect the spikes on one revolving rollers are preferably placed very close to the spikes on a neighbouring roller, e.g. 2 mm.

Furthermore, it is possible to vary the intensity of the spikes both in the axial direction and the circumference of the revolving roller. By means of these parameters, the placement of the spikes in relation to spikes on a neighbouring revolving roller, the number of revolutions for the rollers and the air stream it is possible to adjust the capacity of the forming head according to the invention.

The spikes can according to one embodiment according to present invention be made of a partly or completely flexible material. In this way it is ensured, that if the spikes touches or hits each other or the wall of the forming head, the spikes will not break or snap. This will ensure that the forming head is more reliable in operation and requires lesser maintenance than the known forming heads using non-flexible spikes. Such flexible or partly flexible spikes can e.g. be in the form of bristles or brushes.

Alternatively, the spikes can be made of a non-flexible material. Such spikes will provide a higher force of impact, which is preferred for some kinds of fibre material. Using a non-flexible material for the spikes will thereby ensure that especially recalcitrant agglomerates, lumps and/or shadows are disintegrated.

In any case, the longer the spikes the harder the impact on the fibrous material and the more efficient is the separation of the agglomerates.

In another preferred embodiment according to the present invention the at least one roller in at least one of the distribution unit are detachable mounted. Thereby is it possible to arbitrarily adjust e.g. the closeness of the spikes on the revolving rollers, the length of the spikes and/or the material the spikes are made of simply by replacing, removing or adding one or more of the revolving rollers in a distribution unit.

The adjustment can also be effected by mounting the rollers mutually displaceable in a substantially horizontal plane, whereby it is possible to establish gabs, which allow a bigger amount of fibre material to pass within a given period of time. Alternatively the revolving rollers in a distribution unit can have different lengths and/or dimensions.

The forming head can advantageously be provided with a bottom with a plurality of openings. This bottom can preferably be placed in the distribution step closest to the forming wire, but can within the scope of protection be placed in all, some or none of the distributions units, depending on the used fibrous material and the final product.

If for instance long fibres are to be handled, it is preferred that there is not placed a fixed bottom at the distribution step(s). However, if smaller fibres or particles are to be distributed via the forming head, one or more distribution steps can advantageously be provided with a fixed bottom.

The suction unit placed beneath the forming wire, which preferably is a vacuum unit, will influence the small particles and/or fibres to a higher degree than the longer fibres. The fixed bottom will prevent the small fibres and/or particles from being sucked directly through the revolving rollers and onto the forming wire and will therefore contribute to ensure that products comprising small fibres and/or particles also are homogenous.

The fixed bottom can preferably be in the form of a sieve, net or a grid arranged for placing the fibres and/or particles on the forming wire. In order to ensure the passage of the fibres and/or particles through the bottom of the forming head the bottom can comprise wings, rollers or other scraping or brushing devices, which in an active manner removes fibres from the bottom.

The size of the openings in the mesh or sieve at the bottom of the forming box depends upon the characteristics of the fibres and/particles, which are to be distributed on the forming wire and on the desired product. This is particularly relevant in relation to the use of cellulose fibres in the manufacture of paper products including absorbing products, such as napkins.

When the bottom is in the form of a grid having a plurality of detachable grid elements, the bottom can be easily changed to in order not only to adjust and/or change the capacity of the forming head, but also in order to change the transferring rate of the fibres to the forming wire. In this respect the bottom can contribute in optimising the final product.

The rollers can preferably be placed either horizontally or vertically whereby the spikes will rotate in a vertical plane and a horizontal plane, respectively. This is preferred because of the symmetrically laying down of fibres so that a tissue with homogeneous thickness is formed over the width of the forming box.

In order to arrange the forming head with horizontally oriented rollers for handling of fibres with various abilities it is possible to provide several layer of rollers in each distribution unit. The rollers in each layer can be placed on a row with their longitudinal axis oriented parallel or orthogonal on the movement direction of the forming wire. The longitudinal axis of the rollers can, however, also be oriented in the direction parallel with the movement direction of the forming wire.

According to the invention is has been shown possible to form a fibrous product, where problems are avoided with the variation of the thickness over the width of the product formed on the forming wire. It is anticipated that this surprising homogeneity of the thickness of the created product over the width of the product is due to fact that the rotation of the spike rollers leads the fibres directly down against the forming wire in the direction orthogonally on the surface of the forming wire. Thus in an advantageously embodiment the rollers in each distribution unit are adapted for being rotated around their longitudinal axes with the same rate of rotations, e.g. within an interval of between 200 and 5000 rpm, preferably about 2000-3000 rpm.

However, the rollers can in a different embodiment be adapted for having different rates of rotation in the different distribution steps or simply within a single distribution unit. By allowing the rotational speed to be adjustable, each distribution unit can be made to work at an optimum, even if the unit at different times is supplied with different amounts of materials. In this respect it is also possible to design each distribution steps for materials having special physical properties.

As previously mentioned the spikes on each revolving roller can be distributed both along the longitudinal axis of the roller, and along the circumference of the roller. It is preferred that said distribution is evenly in both directions in order to ensure a homogenous distribution to the forming wire.

It is also possible to use very varying dimensions and revolving rates. It is, however, preferred that the axial distance between the spikes is between 3 and 20 mm, and that the thickness of the spikes is between 0.5 and 10 mm. The length of the spikes will be between 5 and 200 mm, preferably about 100 mm.

Within the scope of the present invention it is also possible to use rates of rotation, lengths of spike and thickness of spike, which lie outside these intervals. By varying the length and the thickness of the roller and spikes it is likewise possible to handle long fibres without the risk that they spin into each other. That is, it will be possible to handle the long fibres and get these down on the forming wire as individual fibres, without being spun into each other.

In order to manufacture final products of very short fibres, i.e. having length of around 2-4 mm, the outer ends of the rollers with the protruding spikes are spaced in order to allow the passage in-between for corresponding spikes on an adjacent roller, e.g. the spikes meshes like a toothed wheel. Hereby it becomes possible to achieve a very homogeneous product with a very homogeneous profile in the sectional direction as well as in the longitudinal direction. It is also possible to handle the short fibres, as the fibres to a higher degree will be retained in the distribution unit, preventing the fibres from falling directly onto the forming wire.

The present application the term spikes will cover an embodiment with largely thread-formed spikes. However, the issue will also cover plate-formed elements, which also can be designated as wings. Such plate-formed wings will primarily be formed with the expanse placed in a plane orthogonally on the rotation axis of the axle. Alternatively the plates can be formed with a slope or be formed like propellers to bring about an upwards or downwards directed action on the fibre cloud. To facilitate the passage of air to the forming head when wing-formed spikes are applied, the wings can be provided with holes. Such holes can facilitate the passage of air. By appropriate choice of revolving speed and form of holes in the rollers the passage of fibres to such holes can be hindered or limited.

In an especially advantageously embodiment according to the invention the forming head comprises four distribution units, placed in succession starting from the distribution unit farthest from the forming wire. It has surprisingly been found that when the first distribution unit comprises one revolving roller, the second distribution unit comprises two revolving rollers, the third distribution unit comprises one revolving roller, and the forth distribution unit comprises a plurality of revolving roller arranged in a substantially horizontal plane, the fibrous material will be completely opened and free from lumps and shadows which again ensures a very even distribution of the fibres on the forming wire.

The top distribution unit are preferably arranged to be able to transfer a relatively higher impact to the fibrous material. Thus it has been found that a single revolving roller having long spikes of e.g. between 50 and 130 mm in length is preferred. In this respect the first distribution unit can have the same or a smaller horizontal cross section than the underlying distribution unit(s). The inventors have shown that a forming head having said construction provides a decidedly beneficial “shower effect” created by the difference in air fluxuation, that distributes and effectively spreads the fibres evenly onto the longer underlying distribution unit(s).

The final product may be made from or at least include natural fibres, such as cellulose fibres, fibres from flax, hemp, jute, ramie, sisal, cotton, kapok, glass, stone, old newsprint, elephant grass, sphagnum, seaweed, palm fibres or the like. These fibres have a certain insulating capacity that may be useful in many applications.

The product may also be made from or at least include a portion of synthetic fibres, such as polyamide, polyester, polyacrylic, polypropylene, bi-component or vermiculite fibres or the like as well as any kind of granular material. Fibreboards with such synthetic fibres may be used for providing the fibre product with certain properties, e.g. absorbent products. Moreover, the fibres may be pre-treated with a fire retardant or a fire retardant may be supplied directly in the fibre mixture, which is blown into the forming box.

Since the forming head according to the present invention is capable of using very long fibres, it is possible to create a stable product, although it is manufactured with a big thickness. This is due to the fact that the long fibres are capable of forming fibrous bindings over a relatively big layer of material, e.g. up to 200-400 mm. The bindings can be crispy hydrogen bindings or elastic bindings, which are established by means of binding material or a combination hereof.

The forming head according to the invention can therefore be used to e.g. manufacture isolation mats from synthetic fibres or natural fibre or mixtures hereof

In this respect the distribution unit closest to the forming wire can optionally comprise end walls, which can be adjusted with respect to the heights in relation to the forming wire. Thereby is achieved the advantage that the thickness of the final product is not limited to a specific maximum height.

The invention will be described in more detail with reference to the accompanying drawing, where

FIG. 1 is a schematic perspective view of a forming head according to one embodiment of the invention;

FIG. 2 shows a schematic side view, partly sectionally, of the forming head shown in FIG. 1,

FIG. 3 shows a schematic side view, of the forth distribution unit shown in FIG. 1,

FIG. 4 shows a schematic side view, of a different embodiment of the forth distribution unit in FIG. 1, and

FIG. 5 a shows a schematic side view of a forming head according to a second embodiment of the invention.

FIG. 5 b shows the embodiment shown in FIG. 5 a in a schematic front view.

In the following FIGS. 1-4 it is assumed by way of example that the forming head according to the invention comprises four distribution units. This are of course in no manner intended to be limiting to the invention, and within the scope of the present invention the forming head can comprise from two to a plurality of distributions units.

In FIG. 1 a forming head 1 according to a first embodiment of the invention is shown. The forming head comprises four independent interconnected distribution units 2, 3, 4 and 5 respectively. Fibres are supplied to the first distribution unit 2 via an inlet 6. A suction unit 7 is positioned beneath a forming wire 8, and the forming head is positioned above the wire. Fibres 9 are air laid on the forming wire 8 to form a web 10 in a dry forming process.

In FIG. 1, the forming head is shown with the interior elements visible in the forth distribution unit 5. However, it is realized that the housing walls may be made from transparent or opaque materials.

Inside each distribution unit 2,3,4,5 revolving rollers are provided with protruding spikes 12.

In the embodiment shown in FIG. 1 the first distribution unit 2 comprises one revolving roller 11, the second distribution unit 3 comprises two revolving rollers 12, 13, the third distribution unit 4 comprises one revolving roller 14, and the forth distribution unit 5 comprises five revolving rollers 15, 16, 17, 18, 19, placed in a substantially horizontal plane parallel to the forming wire 8.

The five revolving rollers 15, 16, 17, 18, 19, which are placed within the forth distribution unit, can be said to make up the bottom of the forming head wherein three revolving rollers 15, 16, 17 are placed by one side wall of the distribution unit and two revolving rollers 18, 19 at the opposite side.

It will be evident for the person skilled in the art that the number of revolving rollers can be adjusted depending on the desired product and the fibres used.

Engines 20, arranged with the possibility for a variable revolution rate, drives each revolving roller, ensuring that it is possible to adjust the revolution rate of the engines dependent of choice of rollers, spikes and the product, which is to be formed.

Each of the revolving rollers 11,12,13,14,15,16,17,18,19 has an axle 21, upon which spikes 12 in form of thread-formed elements are protruding. The spikes 12 are established with a size and a mutual distance, which makes it possible to allow for a passage in-between for corresponding spikes 12 on a neighbouring revolving roller.

The revolving spike rollers are in the embodiment shown in FIG. 1 placed so that the outer ends of the spikes describe circles that do not overlap each other.

The fibres 9 are supplied to the forming head 1 via inlets 6. Said fibres will comprise agglomerates, lumps and/or shadows and when these comes into contact with the spikes 12, the agglomerates, lumps and/or shadows will be disintegrated or shred in order to ensure an even distribution of fibres 9 in the product 10 formed on the forming wire 8.

This is due to the fact that the disintegration of agglomerates of a fibrous material are influenced by strokes from spikes on the revolving rollers, and when e.g. an agglomerate is hit by a revolving spike the impact force will ensure that the agglomerate, at least to some extend, will be forced to open and/or disintegrate.

As this is repeated, not only several times in each distribution unit, but also in the four distribution units, all agglomerates, shadows and/or lumps will be removed in order to ensure an even distribution of fibres 9 in the product 10 formed on the forming wire 8.

The closer the spikes 12 are placed to each other on the revolving rollers 11,12,13,14,15,16,17,18,19, the more efficient will the spikes return agglomerates, lumps and/or shadows to the respective distribution units 2,3,4,5, In this manner the fibre clumps or clusters of fibres are retained by the revolving rollers and separated or disintegrated in a graduated fashion as these retained fibres are returned by the spikes 12 to the distribution unit rather than being sucked down to the forming wire 8 or underlying distribution unit by the suction unit 7.

Fibres are supplied in an airflow to the first distribution unit 2 via an inlet 6. The airflow can be created by means of transport blowers, which are linked with pipes that lead to the distribution unit, but other ways of obtaining the airflow known to the person skilled in the art are within the scope of protection.

In the embodiment shown in FIG. 1 the fibres are primarily led in from each side of the first distribution unit 2, but fibres could also be feed to the distribution unit by means of more inlet pipes on each side of said distribution unit or to several of the distribution units. It is hereby possible to vary the capacity of the forming head by opening and closing the inlet pipes.

As an alternative to the inlet 6 the fibres can be introduced to the distribution unit in question by blowing them into said distribution unit. This will ensure, that the fibres have a substantial velocity upon introduction to the unit, which provides that large concentrations variations throughout the forming head will be reduced or even eliminated, ensuring a more uniform distribution of powder to the web.

The topmost first distribution unit 2 may or may not have a detachable lid 23 to allow inspection and maintenance of the forming head, and to provide the possibility of admitting false air so that a negative pressure does not build up in the forming head and obstructs the continuous flow towards the forming wire obtained by means of the suction unit. Preferably, the lid 23 has an air inlet opening 24 for admitting the false air. The opening may be provided in the lid 23 or any other suitable site on the forming head, e.g. in the axial side of the first 2 and/or subsequent distribution unit, as well as more openings may be provided and favourable.

The uniform distribution is furthermore increased as the revolving rollers retain fibres before they are gradually sucked down via the vacuum from the suction unit to the forming wire. In this way the revolving rollers works as a kind of buffer zone, ensuring, that the fibres do not fall directly onto the forming wire.

Fibres or other product which are to be part of the final web could also be are added to several of the distribution steps of the forming head according to the invention, increasing the capacity of the forming head.

In this respect the fibre material comprising the agglomerates, lumps and/or shadows which requires the highest impact force can be feed to the first distribution step 2, and the fibre material which requires the lowest impact force to the forth distribution unit 5.

FIG. 2 shows a schematic side view, partly sectionally, of the forming head shown in FIG. 1. On the right side of the picture a partial section is shown for schematically illustrating the revolving rollers 11,12,13,14,15,16,17,18,19 and the left side of the picture shows the engines 20.

As is seen the first distribution unit 2 and the third distribution unit 4 both comprises one revolving roller 11, 14 having spikes 12, which covers only about 65% of the sectional area of the distribution unit. In contrast the second distribution unit 3 has the two revolving rollers 12, 13, with spikes that substantially covers the entire area of the respective distribution units.

The forth distribution unit 5 has five revolving rollers 15, 16, 17, 18, 19, placed in a substantially horizontal plane parallel to the forming wire 8. These revolving rollers with belonging spikes will cover the entire bottom of the forth distribution unit 5, through which the fibre material will be released to the forming wire. Since the spikes partly will retain the fibres against the effect from the suction of the suction unit the cloud of fibres, which has been formed inside the forming box of single fibres are split up and mixed in the air stream, are transferred down onto the underlying wire by application of the revolving spike rollers.

FIG. 3 shows a schematic side view of a forth distribution unit 5, according to the invention wherein the spikes 22 on the revolving rollers 15,16,17,18,19 are placed so that the outer ends 23 of the spikes describe circles that do not overlap each other.

This is especially advantageously when the spikes 22 on the revolving rollers are not flexible, as an impact between two revolving and adjacent spikes can cause the spikes to break.

FIG. 4 shows a different embodiment of the forth distribution unit 5, according to the invention to the invention described, wherein the spikes 22 on the revolving rollers 15,16,17,18,19 are be placed so that the outer ends 23 of the spikes describe circles that do overlap each other. As is clearly shown on the figure two adjacent spikes will engage with each other like toothed wheels.

The embodiment shown in FIG. 3 has the advantage that the revolving rollers 15,16,17,18,19 can be placed closer to each other, whereby the fibres can be influenced by more than one spike 12 at a time, providing a higher impact force on the agglomerates, lumps and/or shadows, enabling a better disintegration.

This is especially advantageously when the spikes 22 on the revolving rollers are not flexible, as an impact between two revolving and adjacent spikes can cause the spikes to break.

FIGS. 5 a and 5 b shows a second embodiment 25 of the forming head according to the invention. This embodiment basically corresponds to the first embodiment with a few modifications and for like parts same reference numbers are used.

In FIGS. 5 a and 5 b is assumed by way of example that the forming head according to the invention comprises sixth distribution units. This are of course in no manner intended to be limiting for the invention, and the forming head can within the scope of the present invention comprise from two to a plurality of distributions units.

The forming head shown in FIGS. 5 a and 5 b comprises six independent interconnected distribution units 26, 27, 28, 29, 30 and 31 respectively. Fibres are supplied to the first distribution unit 26 via an inlet 6. A suction unit 7 is positioned beneath a forming wire 8, and the forming head 25 is positioned above the wire. Fibres are air laid on the forming wire 8 to form a web in a dry forming process.

As shown in FIGS. 5 a and 5 b the first, second and third distribution units 25, 26 and 27 have a smaller horizontal cross section than the underlying distribution units, i.e. the forth, fifth and sixth distribution unit 28, 29 and 30.

The difference in the horizontal cross section ensures a fluxuation in the air flow between the distribution units having the smaller cross section and the distribution units with the larger cross section, whereby an un-even air flow is created that will ensure that the fibres are distributed and spread more homogenously onto the underlying distribution unit(s).

Inside each distribution unit revolving rollers are provided with protruding spikes 12.

In the embodiment shown in FIGS. 5 a and 5 b the first distribution unit 26 comprises one revolving roller 32, the second distribution unit 27 comprises two revolving rollers 33, 34, the third distribution unit 28 comprises one revolving roller 35, the forth distribution unit 29 comprises one revolving roller 36, the fifth distribution unit 30 comprises two revolving rollers 37, 38, and the sixth distribution unit 28 comprises three revolving rollers 39, 40, 41 placed in a substantially horizontal plane parallel to the forming wire 8.

The three revolving rollers 39, 40, 41, which are placed within the sixth distribution unit, can be said to make up the bottom of the forming head.

It will be evident for the person skilled in the art that the number and dimensions of the revolving rollers and the corresponding spikes can be arbitrarily adjusted depending on the desired product and the fibres used.

Engines 20, arranged with the possibility for a variable revolution rate, drives each revolving roller, ensuring that it is possible to adjust the revolution rate of the engines dependent of choice of rollers, spikes and the product, which is to be formed.

A single engine 20 drives all revolving rollers in a distribution unit. A synchronous transmission belt (not shown) is used to transmit the force from said engine to the respective revolving rollers. Thereby is obtained the beneficial effect that the revolving rollers can be placed so that the outer ends of the spikes describe circles that overlap each other e.g. meshes like toothed gear. This embodiment has the advantage that the revolving rollers can be placed closer to each other, whereby the fibres can be influenced by more than one spike at a time. This will provide a higher impact force on the agglomerates, lumps and/or shadows, enabling a better disintegration of the fibrous material. Furthermore, when the outer ends of the spikes are transferred in-between each other, it becomes possible to manufacture a fibrous tissue using very short fibres, for instance with lengths down to 3 mm. Hereby it becomes possible to achieve a very homogeneous product with a very homogeneous profile in the sectional direction as well as in the longitudinal direction.

It is of course possible to use individual engines for each revolving roller in one distribution unit and a common engine and a synchronous transmission belt for all revolving rollers in a second distribution unit etc.

It should further be stressed that each distribution unit with attached motor in the forming head is a “plug and go” and can be pulled out and exchanged swiftly by hand, replaced by another distribution unit, removed completely or an additional distribution unit added to the forming head. 

1. A forming head for dry forming a fibrous web, the forming head being positioned above a forming wire opposite a suction unit, wherein the forming head is divided into at least two distribution units detachable mounted in the forming head, the at least two distribution units are arranged one of top of the other and each distribution unit comprises at least one revolving roller provided with protruding spikes.
 2. A forming head according to claim 1, wherein the distribution units in the forming head are in communication with each other such that the upper distribution unit(s) can pass fibrous material to the underlying distribution unit(s).
 3. A forming head according to claim 1, wherein the spikes on the at least one revolving roller in at least one of the distribution units covers between about 30% to about 80%, preferably about 65% of the sectional area of the distribution units seen in relation to the forming wire.
 4. A forming head according to claim 1, wherein the spikes on the at least one revolving roller in at least one of the distribution units substantially covers the entire sectional area of the distribution units seen in relation to the forming wire.
 5. A forming head according to claim 1, wherein at least one distribution unit has the same or a smaller horizontal cross section than the underlying distribution unit.
 6. A forming head according to claim 1, wherein the at least one roller in at least one of the distribution unit is detachable mounted.
 7. A forming head according to claim 1, wherein at least one revolving roller has a different dimension and/or length than the remaining revolving rollers in a distribution step.
 8. A forming head according to claim 1, wherein the forming head is provided with a bottom having a pluralities of openings.
 9. A forming head according to claim 8, wherein the bottom is a grid having a plurality of detachable grid elements.
 10. A forming head according to claim 1, wherein the at least one roller in at least one distribution unit, is placed with the longitudinal axes oriented substantially perpendicularly to the moving direction of the forming wire.
 11. A forming head according to claim 1, wherein the rollers in at least one distribution unit, is placed with their longitudinal axes in the same or in a different orientation in relation to the rollers in one of the other distribution units.
 12. A forming head according to claim 1, wherein the rollers in each distribution unit are adapted for being rotated around their longitudinal axes with the same or different speed of rotations.
 13. A forming head according to claim 1, wherein the spikes are distributed evenly along the circumference of the roller.
 14. A forming head according to claim 1, wherein the spikes in at least one distribution unit, in the longitudinal direction of the roller, are spaced, which allow the passage in-between for corresponding spikes on an adjacent roller.
 15. A forming head according to claim 1, wherein the spikes on the rollers are made of a flexible material.
 16. A forming head according to claim 1, wherein the forming head comprises four distribution units, placed in succession starting from the distribution unit farthest from the forming wire, wherein the first distribution unit comprises one revolving roller, the second distribution unit comprises two revolving rollers, the third distribution unit comprises one revolving roller, the fourth distribution unit comprises a plurality of revolving roller arranged in a substantially horizontal plane.
 17. A forming head according to claim 16, wherein the spikes on the revolving rollers in the first, second and fourth distribution unit substantially cover the entire sectional area of the respective distribution units when seen in a mainly horizontal plane.
 18. A plant for producing a fibrous web wherein the plant comprises a forming head according to claim
 1. 19. A method for dry-producing a fibrous web, using the forming head according to claim 1, and wherein the at least two distribution units is detachable mounted in the forming head and arranged one of top of the other, wherein fibrous material is added to the distribution unit farthest from the forming wire for processing in the forming head, the fibrous material passed from one distribution unit to the underlying distribution unit(s) and the fibrous material is laid on the forming wire for forming the fibrous web.
 20. A method according to claim 19, wherein the at least one distribution unit is removed from the forming head, and a different distribution unit is inserted instead. 